Legionella prevalence in hot spring recreation areas of Taiwan

Abstract

Legionella is a bacterium ubiquitous to aquatic environments. Within the genus a few species are recognized as opportunistic potential human pathogens, especially the species Legionella pneumophila, which causes pneumonia legionellosis. Outbreaks of legionellosis are frequently reported by hotel guests and hospital patients, and are spread through inhaled aerosols of contaminated institutional water systems. Contaminations in hot tubs, spas and public baths are also possible. As a result, in this study, we investigated the distribution of Legionella at seven hot spring recreational areas throughout Taiwan. We gathered data on factors potentially associated with the pathogen's distribution, including environment, facility operation, and physical and microbiological water quality parameters. Spring water was collected from 91 sites and Legionella was detected in 21 (23%). The most frequently detected was L. pneumophila, followed by uncultured Legionella species, Legionella-like amoebal pathogen. Five species, L. bozemanii, L. dumoffi, L. feelei, L. lyticum and L. oakridgenesis, were all detected once. Legionella species were found in water temperatures ranging from 22 to 50 °C. Optimal pH appeared to be between 5.0 and 9.0. The prevalence of Legionella also coincided with the prevalence of indicator microorganisms. Legionella detection was not proportional to the frequency of cleaning. Results of this survey confirm the ubiquity of Legionella in Taiwan spring recreation areas. L. pneumophila, the organism responsible for the majority of legionellosis outbreaks, should be considered a potential public health threat in spa areas of Taiwan.

Introduction

Legionella is a Gram negative bacterium with many species which is ubiquitous in aquatic environments. Only a few species of Legionella, are human pathogens with the potential to cause legionellosis (Fraser et al., 1977; Broome et al., 1979). Human infection occurs through the inhalation of aerosols contaminated by Legionella. No interhuman transmission has yet been found (Catalan et al., 1997). Legionella are able to reproduce at temperatures between 25 and 43 °C and survive in temperatures of up to 55–60 °C; therefore, they thrive easily in naturally and artificially hot water systems (Leoni et al., 2001). Outbreaks of legionellosis are most frequently reported from hotel guests and hospital patients (Rosmini et al., 1984; Meenhorst et al., 1985; Joseph et al., 1994).

The frequency of occurrence of legionellosis has been described in several countries. There are 8000–18,000 cases of legionellosis annually in the United States (Marston et al., 1994, Marston et al., 1997). In Japan, the frequency is much lower, around 20 cases a year during the last few years (Iwamoto et al., 1995). Between 1999 and 2002 Taiwan has had on average 60 cases of legionellosis reported to the Taiwan Center for Disease Control (CDC) each year.

A particular risk factor has recently been identified in the use of hot tubs, spas and public baths (Spitanly et al., 1984; Tolentino et al., 1996; Leoni et al., 2001). In Taiwan, hot spring facilities (e.g., hot tubs, spas and swimming pools) have become an increasingly popular form of recreation. Millions of people in Taiwan enjoy bathing in hot spring tubs. It is important to have the capacity to rapidly detect Legionella in hot spring facilities where people swim and bathe to avoid serious outbreaks.

Cultivation of Legionella is time consuming, but it is the method approved by ISO and many other national standards for water quality determination of Legionella. However, the organisms may be present in a viable but non-culturable form. Their growth on agar media may also be inhibited by other elements in the samples (Hussong et al., 1987; Palmer et al., 1993, Palmer et al., 1995). Direct PCR testing of environmental samples may result in false positives in cases where non-viable cells or exogenous DNA are present. Therefore, new methods have been developed to allow a more reliable characterization of Legionella species (Miyamoto et al., 1997).

To date, little serious consideration has been given to the potential for a large Legionella outbreak in Taiwan and as a result there are little data on the natural occurrence of Legionella in hot spring facilities in Taiwan. This study, therefore, was undertaken to assess the potential of outbreak by describing the current distributions. We used PCR amplification and DNA sequencing methods to allow taxonomic identification of Legionella species. A total of 91 spring water samples were taken from seven prescreened locations between September 2004 and March 2005. To assist with interpretation, we collected other information, including the surrounding environment, operation factors for the spring facilities, and physical and microbiological water quality parameters.